The Arisaema serratum group sensu stricto (Araceae) is a Japanese species complex characterized by a well-developed leaf rachis and long pseudostem. They were previously integrated into one species due to wide infraspecific variation, but were split into about 13 species again in recent monographs. In this group, A. maekawae and A. pseudoangustatum var. pseudoangustatum were recently divided from A. angustatum in the type localities (central Japan). A recent study found some sympatric populations of the three species in western Japan and distinguished them based on qualitative observation. However, there are no quantitative study to delimit the species boundaries objectively. The author collected this quantitative data set in these sympatric populations and found that principal component analysis with this data set can successfully delimit the species boundaries between the three sympatric species.